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How trash, sprawl and a warming world impact Michigan mosquito seasons

mosquito
Credit: Pixabay/CC0 Public Domain

Not all of the quintessential characteristics of a Michigan summer are as pleasant as campfires, cookouts and baseball games. There are the mosquitoes, too.

Those insects' itchy bites are making increasingly early appearances. This year, the first round hit in February, a date so early that Michigan State University entomology professor Edward Walker said it's "almost a ridiculous thought."

Except it isn't. As Michigan winters warm, mosquitoes' active season is expanding and some southern species are appearing here.

"Our ambient temperatures are going up, and that means we have an earlier spring and a longer fall," he said. "I can say without any doubt that the mosquito season in the fall is lasting at least a month longer than it did 20 years ago."

That's very likely related to the state's warming climate, Walker said, but climate change isn't the only way Michigan's environmental woes are impacting mosquito activity. In addition to warming temperatures, extended droughts, degraded habitats, litter and sprawl make the state increasingly welcoming to the buzzy blood suckers.

"There are other things happening maybe in tandem to climate warming that may also be drivers," Walker said. "When you see things happen in your lifetime, like this dramatic increase in the southern mosquito species increasing their range north, I really wouldn't have expected that in my career time, but here we are and it's happening."

Litter creates prime mosquito real estate

Restoring natural environments and picking up trash could help limit mosquito populations. That's because mosquitoes thrive in degraded waterways, said Marie Russell, a postdoctoral fellow at the U.S. Environmental Protection Agency's Oak Ridge Institute for Science and Education in North Carolina.

Russell co-authored a study last year that indicated the Great Lakes region will be more vulnerable to as the climate warms. The study, published in the journal EcoHealth, found warming temperatures, climate change-fueled storm surges and degraded ecosystems could create additional mosquito habitat and contribute to increasing spread of mosquito-borne disease.

There are more mosquito predators—such as minnows or dragonfly larvae—in a healthy environment. Mosquitoes including Culex pipiens, which are common in Michigan and carry West Nile virus, breed in shallow natural waters, so having fewer natural predators could mean more disease, Russell said.

"When everything is working in harmony, it's easy to overlook that those things (in the ecosystem) were really beneficial and providing a service that maybe we weren't aware of," Russell said. "I think it's kind of like that when we think about the aquatic communities in shallow waters around the Great Lakes region. There are these natural predators when the ecosystem is healthy and functioning well."

Other mosquito species such as Aedes aegypti and Aedes albopictus prefer to breed in even less natural environments. Like trash.

Those species are newcomers to Michigan in the last decade and likely don't overwinter here. They can carry Zika, chikungunya, yellow fever, and dengue. They like to breed in small, artificial containers that recently were filled with water, such as bottle caps, cups or other litter. In Venezuela, where those Aedes aegypti mosquitoes are common, a 1995 study found poor trash removal practices were associated with higher numbers of the pests.

"We know that in places where that species is already established, picking up litter is super important for controlling the population," Russell said.

Using insecticide or other large-scale mosquito controls in places that are hard to clean, such as junkyards, could be a strategy.

"We know that chemical insecticides are not great but some of the mosquito-borne pathogens are worse, you could argue, for human health," she said.

Sprawl spreads disease

Culex pipiens mosquitoes—the kind Russell said face fewer natural predators in degraded environments—also thrive in cities and suburbs, Walker said. They like to breed in catch basins, which collect material such as leaves and sticks from storm water pipes. Those basins serve as nurseries for the mosquitoes that carry West Nile virus.

And those suburbs also are welcoming habitats for some of the other animals that can carry the virus, such as American robins.

Communities built after World War II, such as Detroit's first-ring suburbs, are hot spots for West Nile virus because they have lots of catch basins, poor drainage, flat terrain and lots of nesting area for robins, Walker said.

Sprawl also changes animal habitats, Walker said, and can lead to more interaction between people, wildlife and mosquito-borne disease.

A pair of mammals that are increasingly at home in the suburbs as communities sprawl into rural areas, coyote and fox, also drive the spread of a common mosquito-borne disease, dog heartworm.

"We have had an increase in our coyote populations," Walker said. "Coyotes are even suburbanized and to a certain extent urbanized now. And coyotes, of course, are not getting veterinary care. They're dogs, and they can become infected with dog heartworm."

Warmer weather means more disease

West Nile virus is the most common mosquito-borne disease in Michigan. There were more than 200 cases reported between 2018-22. The disease causes fever and other symptoms in about 20% of people who catch it and can sometimes be fatal.

West Nile was introduced in Michigan in the early 2000s, said Michigan Department of Health and Human Services medical entomologist Emily Dinh. It's now endemic, which means it occurs regularly in the state.

There are always a few cases reported, Dinh said, but big outbreaks appear to be dictated by the weather, and they're occurring slightly more often than they used to.

Those are symptoms of climate change. Warmer average summer temperatures are expected to increase both drought and flooding conditions, GLISA climatologists said.

"It's usually associated with hot and dry early summers followed by heavy rains early on," she said, and also could be impacted by land use changes or other dynamics.

Another mosquito-borne disease in Michigan is Eastern equine encephalitis, is rare but serious. It can kill almost a third of people infected and leave more with permanent neurologic damage. There were 16 cases reported in Michigan between 2018-22.

Dinh said the disease is associated with mosquitoes that live in hardwood swamps, a common type of environment in Michigan. People may increasingly encounter the disease because we developed those swamps, she surmised.

There are some steps people can take to protect themselves from mosquito-borne disease, Dinh said, such as layering with clothes and repellent when mosquitoes are active, treating standing water or not letting water get stagnant in buckets, pop cans, birdbaths or other small reservoirs.

But protecting Michiganians from disease ultimately is a community effort, she said. That could take the form of educational efforts, such as signage at parks, or more funding for and participation in mosquito surveillance work, and better access to health care.

"We, humanity, like to think that the mosquitoes are in our habitat when really the mosquitoes have always been here," Dinh said. "It's understanding how human development has interacted with the sort of environment that both we are in and also produced."

Journal information: EcoHealth

2024 The Detroit News. Distributed by Tribune Content Agency, LLC.

Citation: How trash, sprawl and a warming world impact Michigan mosquito seasons (2024, May 13) retrieved 14 June 2024 from https://phys.org/news/2024-05-trash-sprawl-world-impact-michigan.html
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